1. Field of the Invention
This invention generally pertains to a sensing means by which to determine the moment in time that a moving object collides with a collision obstacle that is in cooperative association with a stationary sensor. It particularly pertains to a low-cost sensing apparatus for sensing the arrival of one or more toy vehicles (e.g. racecars) across the finish line on a raceway (e.g. a racetrack).
2. Description of Related Art
There are no prior art methods, structures, apparatuses, or devices published or on the market for utilizing a free collision obstacle in the path of a moving vehicle to electronically sense the arrival of the vehicle at a finish line. Within this disclosure, the meaning of “free” in “free collision obstacle” is that a collision obstacle is not rigidly or pivotally fastened to the raceway, but that the collision obstacle is free to be propelled away from the finish line by the force of a collision with a moving vehicle. What the prior art does use for sensing the arrival of a vehicle at a finish line is a variety of sensing techniques involving sensing apparatus that are fixed to the raceway.
The simplest prior art sensing apparatus comprises a phototransistor embedded in the raceway below the finish line, one phototransistor per lane of a multilane raceway. Overhead illumination is used, wherein race vehicles crossing the finish line interrupt light from the overhead illumination from reaching the respective phototransistor, thus accomplishing an event in the phototransistor that can be sensed directly by electronic means. Undesirable aspects of this approach include the inconvenience of having to supply overhead illumination, the effects that unequal shapes of vehicles have on the interruption of light to the phototransistors, and that background illumination such as camera flashes can affect the timing of the phototransistor's detection event.
More sophisticated prior art utilizes slotted photosensors in conjunction with a trip-lever located in each lane of a racetrack for toy racecars. A racecar reaching the finish line knocks a pivoted lever over. On the pivoted lever is a small optically opaque flag that interrupts the beam in the slotted photosensor, and when the pivoted lever rotates, this flag is thus carried out of the slot in the photosensor. This approach leads to a more expensive structure, as the slotted photosensor has to be prearranged structurally with the flag and to the swing-path of the lever for proper operation. The resulting assembly of a lever arm, a flag, a pivot axle, a slotted photosensor, along with the structure to support these in an operating unit, is large enough to require a large mounting hole be cut through the bed of the racetrack. The advantage of this approach, however, using a slotted photosensor and an optically opaque flag on a pivoting trip-lever, is that it provides for greater precision and accuracy than the phototransistor approach that uses overhead illumination. The slotted phototransistor affords a greater protection from false operation caused by background illumination, and the sensor in each lane of the raceway can be made to operate more consistently, one compared to another. Precision and accuracy of better than 0.001 sec can easily be achieved with this approach.
Mechanical micro-switches have been tried in the prior art but have not been favored due to their lack of timing repeatability. The timing response of micro-switches to actuation events can vary one event to another by over ten milliseconds, even when de-bounced electronically. For vehicles traveling approximately 16 km/hr (approximately ten miles per hour), this can cause errors in finish line event timing equivalent to the time it takes a racecar to travel a few centimeters (just over an inch). For races where the racecars are separated by less than 2 to 3 cm (approximately an inch) approaching the finish line, this error magnitude is unacceptable.
What is needed that is not provided by the prior art are sensing apparatuses and methods that are at the same time: low cost, easy to install, precise and accurate in detection of finish line events, insensitive to ambient lighting conditions, convenient and easy to use, cause little damage to toy racecars, don't cause toy racecars to jump out of their lanes, and actually add excitement to a race.